With over 75 million native speakers worldwide, Korean is the official language of South Korea and North Korea. It is also one of the two official languages in the Yanbian Korean Autonomous Prefecture in People's Republic of China. For over a millennium, Korean was written with adapted Chinese characters known as hanja, and was complemented by phonetic systems such as hyangchal, gugyeol, and idu. There has been debate on the origins of the Korean language. Most historical linguists classify Korean as a language isolate -- a natural language with no other genealogical language relationship -- while a few consider it to be in the controversial Altaic language family which, includes Turkic, Mongolic, and Tungusic families.